(1) Field the Related Art
The present invention relates to a package for high frequency waves and, more particularly, it relates to a high performance package for high frequency waves that enables outputting a large electric current.
(2) Description of the Related Art
Devices and instruments are generally designed as 50Ω type in the field of microwaves.
Similarly, as for packages for high frequency waves that contain elements for high frequency waves and matching circuits, characteristic impedances are generally designed as 50Ω type as viewed from the input terminal and the output terminal. Additionally, the input terminal and the output terminal are normally made to show a same profile and a same size regardless of the level of the flowing electric current. However, signals are more often than not amplified depending on the element circuits for high frequency waves contained in a high frequency package, a large electric current flows to the output terminal if compared with the input terminal.
For example, if the characteristic impedance of a feed-through section sandwiched between 0.6 mm-thick ceramic pieces is 50Ω, the line width is 0.6 mm and the limit for metal thickness is about 0.1 μm for achieving hermetic condition when sandwiched between ceramic pieces. Then, a large ohm loss is produced when an electric current is flowed to a line showing such a relatively high resistance. For this reason, there arises a problem that the applied voltage is not effectively conveyed to a semiconductor chip and the line can be fused by Joule heat generated when an electric current flows through the resistance components at the output terminal side to make it impossible to obtain a sufficient current capacity.
GaAs FET packages where the input side gate terminal is made to show a small width to raise the impedance so as to be used as part of a noise factor matching circuit are known and disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 7-94649. However, such a package also has high resistance components at the output side to make it impossible to obtain a sufficient current capacity and hence can give rise to the above described problem. Additionally, such a package is also accompanied by a drawback that the high frequency characteristics are damaged when the line width of the input terminal or the output terminal is changed abruptly.
In view of the above identified problems, it is therefore the object of the present invention to provide a high performance package for high frequency waves containing a high frequency electronic circuit that can secure a sufficient current capacity at the output section and shows good frequency characteristics.
In an aspect of the present invention, the above object is achieved by providing a package for high frequency waves comprising: an hermetic box-shaped high frequency package containing a high frequency electronic circuit in the inside and shielded by a conductor; an input terminal and an output terminal partly led out to the outside of the high frequency package; an input side feed-through section having one of its opposite ends connected to the input terminal and the other end connected to the high frequency electronic circuit and having a predetermined characteristic impedance; and an output side feed-through section having one of its opposite ends connected to the output terminal and the other end connected to the high frequency electronic circuit and having a characteristic impedance lower than the characteristic impedance of the input side feed-through section as viewed from the output terminal side.
Thus, according to the present invention, it is possible to raise the current capacity at the output side of a package for high frequency waves by having line width wider, that is having the characteristic impedance of the output side feed-through section lower than the characteristic impedance of the input side feed-through section within a range that allows matching the internal high frequency circuit.